^ your issue with going below 80Hz for your fronts may be related to your speaker quality and your crossover slope. You can't talk about crossover settings without discussing the slope.
The RE XXX "midwoofers" are built like tanks and should play cleanly down to 56Hz, which is where I would set my HPF and LPF points for SQ if you have enough of a slope. I run my 6.5's down to 56Hz with 24dB/oct and they are 2001 Oz -180's.
If you must use a bass boost on the head unit, you may need a higher slope, around 63Hz or maybe even 80Hz if the slope is only 12dB/oct. Problem is you start getting muddy midbass response from the sub. Sometimes you can combine a HU crossover and an amp crossover to increase slope.
List all of your equipment, take pics of the install, and we can suggest some crossover points to try once we know what you can actually do with your available settings. I recommend deadening and sealing of the door locations for those massive midwoofers, including some sturdy resin coated MDF mounting baffles.